Defrosting system



Jan. 3, 1950 H. H. CURRY 2,492,970

DEFROSTING SYSTEM Filed Oct 6, 1943 IN V EN TOR.

HERMAN H. CURRY i Patented Jan. 3, 1950 DEFROSTING SYSTEM Herman H.Curry, Morristown, N. J.

Application October 6, 1943, Serial No. 505,141 6 Claims. (01. 62-4)(Granted under the act of March a, 1883, as amended April 30, 1928; 3700. G. 757) The present invention relates to improvements inrefrigerating machines of the compressorcondenser-evaporator typewherein hot gas or liquid refrigerant is used for defrosting coolingunits subject to the collection of frost thereon.

More specifically the invention contemplates the use of the hotrefrigerant to supply sufficient heat to defrost the cooling unit inrefrigerating machines having a hermetically sealed refrigerant systemwithout resorting to the use of auxiliary valves. It also contemplatesthe use of the refrigerant collected in the cooling unit during thedefrosting process in cooling the said unit during the initial operationof the refrigerating system. It further contemplates controllingoperation of the air circulating means until after the temperature ofthe cooling unit, heated for defrosting, drops to the temperature of thespace cooled thereby.

A hermetically sealed refrigerating system is desirable to preventleakage of gas and to prevent the entrance of moisture into the system.This is particularly true in marine refrigerating systems using Freon asa. refrigerant. Automatic defrosting is also desirable in such systemsand especially in quick freezing applications.

In a conventional system, the compressor may be controlled as a functionof suction pressure and the amount of liquid refrigerant released to theexpansion coil maybe controlled by a thermostatically operated valve asa function of the temperature at the suction end of the expansion coil.These controls each have parts which cannot be serviced or replacedwithout opening the Freon-containing system. Automatic water defrostingfor such systems involves drainage problems and the automatic hot gasdefrosting heretofore used requires additional control valves with theattendant possibility of leakage and also necessitates opening thesystem for servicing the same.

Those refrigerators of the factory-assembled household type using ahermetically sealed system in which an orifice or a capillary tube isused to control the flow of refrigerant to the cooling unit arecontrolled by means of a thermostatic switch in the compressor motorcircuit, said switch being responsive to the temperature of therefrigerated space. This system greatly reduces the probability that therefrigerating machine will require repairs necessitating opening thesealed system. However, this system has not been used in largerfield-assembled units because the amount of charge of Freon is criticaland must be closely controlled for the particular size and type ofsystem. Moreover, such systems are not capable of defrosting the coolingunit by use of the hot refrigerant without the use of additionalauxiliary equipment.

It is the object of this invention to obtain hot gas or liquiddefrosting in a hermetically sealed refrigerating system using acapillary tube to control the flow of refrigerant to the cooling unitand not critical as to size of charge within comparatively wide limits.

Another object of this invention is to use hot gas or liquid refrigerantto defrost the cooling unit of a refrigerating system without the use ofvalves.

- Another object of this invention is to utilize the refrigerant passedinto the cooling unit during the defrostng operation to cool theevaporator during the initial operation of the compressor.

Another object of this invention is to reduce the pressure on thepressure side of the compressor to facilitate the starting thereof.

Another object of this invention, is to delay operation of the aircirculating means for the cooling unit until after the compressor hashad time to reduce the temperature of the cooling unit to that of therefrigerated space.

Another object of this invention is toso mount and house the coolingunit that defrosting is facilitated.

Other objects of the invention will be more fully disclosed in thefollowing specification and claims:

In the drawing, the figure is a diagrammatic illustration of arefrigerating system embodying the invention.

Referring to the drawing, depicting a refrigerating system in which thecompressor-condenser unit is, in practice, hermetically sealed therefrigerant compressor I evacuates refrigerant vapor from the coolingunit and discharges it into the condenser 2 where the gas is liquefied.This hot liquid refrigerant is then collected in storage tank 3 fromwhich it is led by means of conduit 14 to an orifice or capillary tube 4which in turn feeds the liquid refrigerant under reduced pressure to thecooling unit, in a refrigerated space R, where in normal operationsufficient heat is absorbed to vaporize the liquid. This vapor thenpasses to the compressor inlet by means of conduit I2.

The cooling unit is composed of an expansion coil 5 and a storagechamber 6. The inlet end of said coil is connected to the capillary tube4 by means of conduit I5 and the outlet end is 3 connected to thechamber I. This chamber may drain through trap II back into the inletend of coil I. The upper part of chamber 6 is connected with the inletof the compressor I by means of conduit I2. Defrosting of the coolingunit is facilitated by the use of an approximately horizontalarrangement of the expansion coil 5,

culates air through passage II over the cooling unit.

Compressor motor II and fan I are connected in parallel to a source ofelectric power and a thermostatic switch I, exposed to the temperatureof a space refrigerated by the cooling unit. controls the supply ofpower thereto. This switch is of a type well known in the art and it ispresumed suflicient to represent the same diagrammatically. It may beset to open the circuit at some predetermined low temperature and toclose it at a selected higher temperature.

The operation of the system is as follows. Assuming the compressor I isin operation and the temperature of the refrigerated space isapproaching the lower temperature setting of thermostatic switch 8 thentank I will contain all excess refrigerant as a hot liquid underconsiderable pressure. The space above the liquid will be fllled withgaseous refrigerant at a temperature corresponding to the pressure.Chamber 6 will contain only refrigerant vapor at a temperature slightlyabove that corresponding to the suction pressure of the compressor I.This pressure diflerential will cause a flow of liquid refrigerantthrough the capillary tube 4. Fan I is circulating air over coil 5.

When the temperature reaches the lower setting of thermostatic switch 8,the switch opens, stopping the motor I3 and fan I. Hot refrigerantcontinues to flow from tank 3 to coil 5 and the pressure in coil 5,chamber i and tube I2 begins to increase with part of the liquidrefrigerant entering coil 8 vaporizing at increasing temperature andpressure until most of the liquid refrigerant has been collected in coil5 and chamber 6. Heat is carried from tank 3 to co l 5 by hot liquid, orby liquid remaining in tan 3 vaporizing and condensing at lowertemperature in coil 5 and as fan 'I is not operating, heat is notcarried away fromcoil i but is held by the housing or inclosure 9,resulting in defrosting said coil each time the compressor I stops. Aslong as both gas and liquid are present on both the hot (compressor) andcold (evaporator) sides of the system, liquid will evaporate on the hotside and vapor will condense at corresponding pressure on the cold side.this process continuing until (1) temperatures equalize, (2) cold sidefills with liquid, or (3) all liquid is evaporated from the hot side.Since each operating cycle is perhaps less than one hour long, only asmall amount of defrosting will be required. This defrosting operationis expedited by housing 9 which prevents loss of heat from the coolingunit by connection currents. As each cycle of operation will becomparatively short, only a 4 limited amount of moisture will collect asfrost on coil 5 and may be effectively melted by the excess liquidrefrigerant collected in tank 3 during the operating cycle.

When the temperature in the refrigerated space rises to the uppersetting of thermostat 8,

compressor I is started and, as condenser and suction pressures haveequalized, operation begins at higher-than-normal capacity, and thepressure against which the compressor must start is materially reduced.As flow through the capillary tube 4 is reduced because of the lowerpressure differential, condenser pressure increases and suction pressuredecreases. In explanation of this statement, it must be first borne inmind that the capillary tube 4 is proportioned to pass the normal outputof the compressor under normal condenser pressure and a normally lowevaporator pressure. Thus, in the starting condition assumed, underwhich there is a lower-thandesigned pressure differential, the flowthrough the capillary tube will be below normal, and because of therelatively high suction pressure the condenser capacity will be abovenormal. Therefore, as stated, condenser pressure will increase and,eventually, suction pressure will decrease to normal designed values.Liquid refrigerant in chamber 6 flows back into coil 5 and is vaporized,the vapor compressed, condensed and stored in tank 3 until normaloperating conditions are restored.

A time delay relay II, of which there are many suitable typescommercially available and so well known in the art that in the presentinstance it is presumed sufficient to present the same diagrammatically,may be placed in the circuit of the fan I to delay starting the sameuntil after the compressor I operates a sufllcient length of time toinsure that the temperature of coil 5 is below that of the refrigeratedspace before air is circulated therein. The refrigerant collected inchamber 6 during the defrosting operation provides more than normalcapacity for a period of time after defrosting for quickly reducing thetemperature of the refrigerated space if such temperature is abovenormal as is customa y after filling the refrigerated space with warmmaterial.

While I have described the preferred form of my invention 1 do not wishto limit myself to the precise details as shown but wish to avail myselfof such variations and modifications as may come within the scope of theappended claims.

The invention described herein may be manufactured and used by or forthe Government of the United States of America for governmental purposeswithout the payment of any royalties thereon or therefor.

I claim:

1. A defrosting refrigerating system including a motor, a compressordriven thereby, a condenser, a storage tank connected to said condenser,a cooling unit and a capillary tube connecting said tank and said unit,said" unit comprising, an expansion coil and a storage chamberpositioned above said coil, means connecting each end of said coil tosaid chamber, said unit receiving hot refrigerant during cessation ofoperation of said compressor, said unit constituting a reservoir forsupplying the system with refrigerant upon resumption of operation ofsaid compressor, and a conduit conducting vapor from said chamber tosaid compressor.

2. An intermittently operated refrigerating system comprising a motor, acompressor driven to said condenser, a cooling unit, said tank and uniteach having a capacity sufllcient to hold all of the refrigerant; a.capillary tube connecting said tank and unit; said unit comprising anexpansion coil and a chamber above the same; a substantially U-shapedtrap connecting the bottom of said chamber to one end of said coil; saidcoil being connected at its other end to the bottom of said chamber at apoint spaced from said trap; and a conduit connecting the top of saidchamber and said compressor, whereby said unit receives hot refrigerantthrough said tube when the compressor is inoperative thereby defrostingsaid unit.

3. An automatic defrosting intermittent-cyclically operatedrefrigerating system comprising a compressor, a condenser connected tosaid compressor, a tank connected to said condenser, an evaporatingcoil, flow restricting means connecting said tank and said coil, saidmeans includin a liquid seal at the end of said coil connected to saidflow restricting means to prevent bypassing said coil when operatingdry; a chamber positioned at a slightly higher elevation than said coil;means connecting said coil to the bottom of said chamber, and a conduitconnecting the upper part of said chamber to said compressor, wherebythe refrigerant is circulated in said coil when operating flooded.

4. A defrosting mechanical refrigerating system comprising a compressor;a condenser connected thereto, and a storage tank connected to saidcondenser; a cooling unit; said unit comprising an evaporator coil and astorage chamber above said coil; said coil having an inlet end and anoutlet end; flow restricting means connecting said tank and the inletend of said coil; means connecting the outlet end of said coil to saidchamber; said last mentioned means comprising a trap; wherebyrefrigerant can circulate in'said coil by convection when said unit isflooded. to cause entering liquid and vapor to flow through the coil toinsure uniform distribution of refrigerant and a minimum of localizedfrosting when said unit is operating dry; and means connecting the topof said chamber and said compressor.

5. In a mechanical refrigerating system arranged for automaticdefrosting, a refrigerated space, a cooling unit therein; an inclosurefor said unit within said space; said inclosure having openings on itslower side arranged to prevent the loss of heat during the defrosting ofsaid unit; means for flooding said cooling unit with hot refrigerant fordefrosting said unit; a fan for circulating air over said unit; andmeans for rendering said fan inoperative during the defrosting of saidunit.

6. The refrigerating system of claim 5 that includes means for delayingoperation of said fan, for a predetermined period after the end of thedefrosting period.

' HERMAN H. CURRY.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS

